Preparation of Porous Thermoset Polyurethane with Supercritical CO2 as Non-solvent

Abstract

Most of porous polymer materials are mainly prepared by solution phase inversion method. The de-mixing process can be initiated by diffusive solvent/non-solvent exchange of binary, ternary or multicomponent mixture. Recently, supercritical CO2 (ScCO2) is used as a non-solvent to prepare porous polymers. ScCO2 possesses excellent properties, such as environmental friendliness, liquid-like density and gas-like diffusivity in comparison with conventional liquid non-solvents. Porous polyurethane was prepared from polymer/N-dimethylformamide (DMF) solution using a supercritical fluid-phase inversion process in which carbon dioxide acted as the non-solvent. The effects of time delay, casting temperature and ratio of polyol/chain extender (POL/CE) on the membrane morphology and structure (size and distribution of cells and pores, thickness of dense layer and porosity) were studied. According to the results, a minimum time delay of 120 min was determined for formation of a suitable structure. The dense layer of 77.6 μm thickness was decreased to 43.1 μm by lowering casting temperature from 55°C to 35°C. The ratio of POL/CE influenced the thermodynamic and kinetic properties. A decrease in POL/CE ratio led to formation of smaller and uniform cells and increased porosity. On decreasing the ratio of POL/CE from 2 to 0.25, the mean diameter of the cells at 6.3 μm dropped to 3 μm.

Keywords

• phase inversion
• thermoset polyurethane
• cells and pores size distribution
• nucleation and growth
• spinodal de-mixing